The present invention relates to a liquid sealing resin composition for sealing slight gaps between a substrate and an IC chip and a fused spherical silica which can be used for the composition.
Demand for high performance and functionality in electronic equipment is increasing with the advent of the multimedia age. In view of this, the shape of IC packages used in electronic equipment tends to be small, thin and of a multiple pin structure. Semiconductor chips are molded by sealing the entire IC chip with an sealant in order to protect fine and complicated electronic circuits formed on the surface thereof from dust or moisture in the air. At present, the material that is most commonly used as an sealant for semiconductor IC chip, is an epoxy resin sealant. This epoxy resin sealant is roughly classified into an epoxy resin sealant for transfer molding and a liquid epoxy resin sealant. The sealant mainly used at present is the epoxy resin sealant for transfer molding, and the use of liquid epoxy resin sealant has heretofore been limited.
However, recently this liquid epoxy resin sealant is beginning to be used as an sealant for the most advanced semiconductor devices, for example, P-PGA (Plastic Pin Grid Array), P-BGA (Plastic Ball Grid Array), flip chip or CSP (Chip Size Package or Chip Scale Package). Of these, many CSPs have a smaller and more complicated structure than conventional devices. The gaps between a substrate and an IC chip in CSPs have been conventionally about 75 to 100 xcexcm. However, in recent years, bump size has become small due to the narrow pitch resulting from a multiple pitch structure, and devices having gaps of about 30 to 50 xcexcm are becoming more common. In order to seal these very advanced semiconductor devices, a fine process-ability is required, and as a sealant which can meet this requirement, there has been a demand for development of a liquid epoxy resin sealant having excellent gap permeability.
On the other hand, the conventional liquid epoxy resin sealants have a problem in that stress generated due to difference between the coefficients of linear expansion of the liquid sealant and an IC chip need to be reduced in order to increase the reliability of the sealant. As a method for solving this problem, there is a method of decreasing the coefficient of linear expansion by blending a large amount of silica filler in the liquid epoxy resin sealant, and as a method for solving the problem of fluidity due to this blend of large amount of silica filler, many methods have been proposed in which finely fused spherical silica having excellent low viscosity characteristics is used (for example, Japanese Patent Application Laid-open Nos. Hei 2-59416, and Hei 2-199013).
However, it is difficult to say that the conventional liquid epoxy resin encapsulants have high reliability with the possibility of filling a large amount of silica fillers, and also sufficiently have a gap permeability which seals a slight gap between a substrate and an IC chip in the most advanced semiconductor devices. For this reason, development of a liquid epoxy resin encapsulant having high reliability and also having decreased viscosity, and a silica filler for a liquid encapsulant, that imparts this performance from the silica filler side, has been demanded.
Accordingly, an object of the present invention is to provide a liquid sealing resin composition having sufficiently low viscosity for sealing slight gaps between a substrate and an IC chip and also having high reliability, and fused spherical silica filler to be filled therein and a method for producing the fused spherical silica.
As a result of extensive investigations, it has been found that a liquid sealing resin composition obtained by blending silica particles having specific particle size characteristics obtained by subjecting fused spherical silica to wet treatment under specific conditions to make the surface of the particles smooth, with an epoxy resin or silicone resin which is liquid at normal temperature can overcome the above-described problem, has a sufficient low viscosity for sealing a slight gap between a substrate and an IC chip, and also has high reliability. The present invention has been completed based on this finding.
More specifically, the present invention provides a fused spherical silica having a maximum particle size of 45 xcexcm, an average particle size of 3 to 10 xcexcm, and a ratio of the specific surface area Sw1 of the particles to a theoretical specific surface area Sw2 of the particles, Sw1/Sw2, of 1.0 to 2.5, the surface of the particles being smooth.
The present invention also provides a method for producing the fused spherical silica, which comprises subjecting to wet treatment a mixture of fused spherical silica formed in oxygen-combustible gas mixed flame and an auxiliary for removing fine particles adhered on the fused spherical silica, thereby separating and removing the fine particles adhered on the surface of the fused spherical silica.
The present invention further provides a liquid sealing resin composition comprising (A) a liquid epoxy or silicone resin, and (B) a fused spherical silica filler having a maximum particle size of 45 xcexcm, an average particle size of 2 to 10 xcexcm, and a ratio of th specific surface area Sw1 of the particles to a theoretical specific surface area Sw2 of the particles, Sw1/Sw2, of 1.0 to 2.5, the surface of the particles being smooth.
The fused spherical silica filler of the present invention has specific particle size characteristics such that the particle surface is smoothed by subjecting the fused spherical silica to wet treatment under specific conditions. Therefore, the fused spherical silica can be blended in high proportion with an epoxy resin or silicone resin which is liquid at normal temperature, and can minimize the coefficient of linear expansion of a liquid sealing resin composition. As a result, the fused spherical silica can impart high reliability. Further, the liquid sealing resin, even if it contains the fused spherical silica in high proportion, has low viscosity, and therefore has good gap permeability.